In communication systems, for example, mobile radiotelephone networks or wireless subscriber line systems, methods for spatial subscriber separation are known, e.g. from DE 197 13 666. In such SDMA (space division multiple access) systems, several communication connections can be supported in a common channel, whereby the channel in FDMA/TDMA systems (frequency-/time-division multiple access) is described by a frequency band and a time slot. For this purpose, adaptive antennas are used at the transmission side, e.g. in base stations of mobile radiotelephone networks. By means of these adaptive antennas, radiation or beam shaping can be used to form several radiation lobes coordinated with the respective position of the receiving radio station, e.g. mobile stations of mobile radiotelephone networks. The spatial resolution used for the separation of subscriber signals takes place by means of these radiation lobes, which are independent of one another.
The transmission path from a base station to a mobile station is called the downward path, and the transmission path from a mobile station to a base station is called the upward path. The spatial subscriber separation by means of radiation shaping is used to particular advantage in the downward path, since for reasons of cost it is preferable to provide only the base station with an antenna means consisting of several individual sensors.
A spatial subscriber separation results in increased capacity in mobile communication systems, since, in addition to other subscriber separation methods TDMA, FDMA or CDMA, a larger number of communication connections can be supported, for the same required bandwidth.
In addition, in communication systems with SDMA subscriber separation the problem occurs with the selection of a suitable channel for an additional connection due to a connection setup or due to a handover procedure from an adjacent cell. For this purpose, it must be assessed whether and to what extent several subscribers operating in the same channel can be spatially separated by means of radiation shaping, i.e. whether for example their dominant directions of incidence are not located too close to one another.
Both for the assessment of the spatial separability of several subscriber connections and also for the calculation and updating of the radiation shaping coefficients after the channel allocation, estimated values concerning spatial parameters of the transmission channels between the subscribers and the base station are required. One possibility for modeling spatial transmission channels is to postulate the existence of a finite number of discrete propagation paths between the mobile and the base stations. The corresponding spatial parameters are given alongside the number of paths by means of the directions of incidence and complex-valued transmission factors of each path. A method for the estimation of these parameters is known from DE 195 11 752; further algorithms of this type can be found in the relevant literature under the trade names MUSIC, ESPRIT and Unitary ESPRIT.
However, the aforementioned methods lead to a high computing expense and high sensitivity to antenna flaws, and fail completely in spatially diffuse scenarios that can no longer be described by a finite number of discrete propagation paths, but rather only by a continuous spectrum of incidence.